Fixing damaged knees is tricky because the form of cartilage found in the joints does not easily regenerate and in some cases total joint replacement is the only option.

修复受损伤的膝盖是一件很复杂的事情，因为关节上的软骨是很难再生的，在一些情况下对关节进行整体更换是唯一可行的办法。

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Though most people eventually recover from joint injuries, damage to the cartilage can't be reversed and can only get worse.

虽然大部分人的关节伤势最后都会复原，但软骨受损却是不可逆的，只会继续恶化。

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Regeneration activity relied on the host's supply of cells to the joint, local tissue response, and functional stimulation to recreate the entire surface of the joint cartilage together with the bone.

再生活动依赖于宿主对关节的细胞供应、本地组织响应与功能刺激以重新建立关节软骨的完整表面以及相关骨骼。

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Joints need cartilage for smooth movement and to absorb shock when you put pressure on a joint.

VOA: special.2010.05.19

This return to normalcy occurred just four months after the surgical procedure, with newly grown cartilage fully covering the joint surface.

VOA: standard.2010.08.11

The disease causes cartilage- protecting joint surfaces to degrade, allowing painful bone-to-bone contact.

VOA: standard.2010.08.11

No space -- meaning no cartilage between the two bones that make up the knee joint -- can cause tremendous pain.

CNN: What you need to know about total knee replacement